1. Field of the Invention
The present invention relates to a method and an apparatus for processing engine valves, and particularly to a processing method and apparatus which are used when used hollow bodies filled with metallic sodium (Na), such as a metallic sodium engine valves or the like employed as valves for internal combustion engines, is disposed of.
2. Description of the Related Art
Recently, requirements on automobile engines are becoming increasingly higher toward better efficiencies, lower fuel consumption, lighter weight, and lower noise in view of tightening regulations (for example, the U.S CAFE regulations and the like). As a result, requirements placed on engine valves have also become tighter for higher operating temperatures, increases in the number of valves used, and decreases in their weight, because an increasing number of engines now burn fuel at leaner air-to-fuel ratios.
One of the most effective means among solutions to such problems is a hollow engine valve filled with metallic sodium (Na). As shown in FIG. 3, a metallic sodium-filled hollow engine valve 1 achieves lighter weight by having a hollow inner cavity in the valve body 2. Due to reduced kinetic energy losses, it also shows reduced fuel consumption and is more quiet because noise is reduced when the valve is seated. Furthermore, the hollow engine valve also achieves higher heat transfer efficiency with metallic sodium (hereinafter referred to as "metallic Na") filled in the hollow valve body. Metallic sodium exhibits characteristic properties of a low specific gravity, a low melting point and a high heat transfer coefficient, so that the hollow engine valve filled with metallic Na can deal with higher temperatures of combustion gas.
The use of the metallic Na-filled hollow engine valve 1 has been gradually increasing mainly for high-end models of automobiles, and is now spreading for also mid-range cars with increasing numbers of valves used. Metallic Na is extremely active and dangerous, so that insertion or filling of metallic Na is carried out under strict control during the manufacturing stage. After the car is sold to the final user, however, such metallic Na-filled hollow engine valves are discarded, and may be cut off together with conventional solid engine valves and come into contact with water at a service garage for regulatory or periodical inspections or at a wrecking yard. In such cases, explosion may occur due to heat evolution and generation of dissolution gas, and alkaline water is violently produced as caustic soda is produced. Products of such chemical reactions cause burn and dermatopathy, and when a product Gets into the eye, serious damages such as ablepsia or blindness arise.
Accordingly, as a conventional method for processing metallic Na-filled engine valves, such engine valves which are apparently filled with metallic Na are separated and collected, and then these metallic Na-filled engine valves are carefully cut off under dry conditions by means of a grinder cutter, saw or the like provided with a long handle while keeping a certain distance away from the operator. Then, as shown in FIG. 4, these engine valves thus cut off are thrown into a container 5 filled with water 4 from a distant place, whereby metallic Na reacts with water in accordance with the following chemical equation to produce aqueous NaOH and H.sub.2 gas 6. EQU 2Na+2H.sub.2 O.fwdarw.2NaOH+H.sub.2
Then, the hollow valve body 2 now containing no Na is taken out from the container after the reaction is completed for further processing.
However, the conventional method of processing engine valves filled with metallic Na involves the following problems:
I. Since the engine valves are mechanically cut off one by one prior to underwater treatment, PA1 II. Since the engine valves are thrown into water,
(1) it is difficult to carry out the whole operation safely, PA2 (2) Na ignites and scatters, forming a jet, due to heat at the time of cutting, and PA2 (3) if fine powder of metallic Na formed and scattered at the time of cutting or fine powder of Na.sub.2 O produced by the reaction of Na with the atmospheric gas gets into the eye, sodium hydroxide (NaOH) is produced by the reaction of the fine powders with tear (H.sub.2 O) as expressed in the following equations: EQU 4Na+O.sub.2.fwdarw. 2Na.sub.2 O EQU Na.sub.2 O+H.sub.2 O.fwdarw.2NaOH PA2 (4) the metallic Na left inside a valve violently produces H.sub.2 gas. The H.sub.2 gas may catch fire, and there exists a danger of hydrogen explosion when such engine valve is treated in a closed room which happens to be badly ventilated. PA2 (5) Since the specific gravity of Na flowing out of a valve after the valve has been cut off is smaller than that of water, Na floats on the surface of water and leaps on it to form a red-hot molten metal. H.sub.2 produced from water is absorbed by the molten metal, and as a result, the red-hot molten metal itself explodes and scatters, so that it is required for the operator to be several meters away from the container for processing the engine valves.
and as a result, eye irritation is caused.